Warbling Wailing Alarm Siren Circuit

2016-02-18 18:59

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This alarm siren circuit give continuous frequency sweep, a warbling sound. The warbling period is about 6 seconds, 3 seconds for frequency sweeping up and 3 seconds for frequency sweeping down. You can change the warbling frequency of this alarm siren by changing the C1 capacitor value. You can vary the value between 10 uF to 47 uF and get an interesting effects.This circuit simulates the sound of an American police siren. IC2 is wired as a low frequency astable that has a cycling period of about 6 seconds. The slowly varying ramp waveform on Cl is fed to pnp emitter follower Ql, and is then used to frequency modulate alarm generator IC1 via R6.IC1 has a natural center frequency of about 800Hz. Circuit action is such that the alarm output signal starts at a low frequency, rises for 3 seconds to a high frequency, then falls over 3 seconds to a low frequency again, and so on ad infinitum.This alarm siren circuit works with 5-15Vvoltagesource, but I recommend 5-9voltsas the best result. Above 12volts, the 555 IC would suffer self-heating and this may shorten its lifetime. Finally, this alarm siren is simple and there would be a lot of fun to make it works.